UNIVERSITY  OF   CALIFORNIA  Agricultural  Experiment  Station 

««.■    ■    w^wf     ***■     .«»*»•**•■•  «••■»■-  BENJ.    IDE    WHEELER.    PRESIDENT 

COLLEGE   OF  AGRICULTURE 

THOMAS    FORSYTH    HUNT,  Dean  and  Director 

BERKELEY  H-    E-   VAN    norman,   Vice-Director   and    Dean 

University    Farm    School 

CIRCULAR  No.  129 

(May,  1915) 

THE  CONTROL  OF  CITRUS  INSECTS* 

By  H.  J.  QUAYLE 


FUMIGATION  FOR  SCALE  INSECTS 
Fumigation  is  the  most  satisfactory  treatment  for  the  control  of 
scale  insects  on  citrus  trees.  The  denseness  of  foliage  and  compactness 
of  growth  of  citrus  trees  make  them  well  suited  for  a  gas  treatment 
within  an  enclosed  tent  covering.  Most  citrus  growers  are  not  so 
directly  interested  in  the  details  of  the  fumigation  processes  because 
such  work  has  been  usually  done  by  contract,  by  the  local  Fruit 
Growers  Exchange,  or  by  an  association.  However,  the  growers  them- 
selves should  understand  enough  of  the  essentials  of  the  fumigation 
work  to  pass  proper  judgment  on  the  character  of  such  work.  As 
compared  with  other  necessary  operations  in  the  citrus  grove,  such  as 
cultivating,  irrigating,  pruning,  and  fertilizing,  most  growers  know 
the  least  about  fumigating.  The  following  account  aims  to  give  a 
practical  consideration  of  the  more  important  facts  of  the  fumigation 
process. 

Fumigation  by  Contract. — A  large  part  of  the  fumigation  at  the  present  time 
is  done  by  individuals  who  make  a  business  of  such  work.  They  possess  one 
or  more  sets  of  tents  and  other  necessary  appurtenances,  and  contract  to  do  the 
work  for  a  stipulated  amount.  Usually  this  amount  is  for  the  cost  of  covering 
the  trees,  and  an  extra  charge  is  made  for  the  acid  and  cyanide.  These 
chemicals  are  generally  purchased,  however,  from  the  fumigator,  who  is  in  a 
position  to  buy  the  materials  in  large  amounts  and  thus  effect  a  saving  in  cost. 

Fumigation  by  the  Exchange. — The  local  exchange,  an  organization  primarily 
for  the  marketing  and  selling  of  the  crop,  often  does  the  fumigating  for  its 
members.  In  such  cases  the  work  is  done  about  at  cost  plus  the  wear  and  tear 
on  equipment. 

Fumigation  by  Associations. — In  some  sections  fumigation  is  carried  on  by 
an  association  of  the  growers,  who  effect  an  organization  for  the  primary  pur- 
pose of  pest  control.  Successful  organizations  of  this  kind  are  the  Co-operative 
Fumigation  and  Supply  Company  of  Upland,  and  the  Growers '  Fumigation  and 
Supply  Company  of  Pomona.     These  associations  also  handle  fertilizers  and  farm 


*  Paper  No.  3,  Citrus  Experiment  Station,  College  of  Agriculture,  University 
of  California,  Riverside,  California. 


implements.  They  have  their  own  fumigation  equipment,  spray  machinery,  and 
materials  for  controlling  pests,  and  the  work  is  done  under  the  supervision  of 
a  manager,  who  is  elected  by  the  members. 

Fumigation  by  Private  Individuals  or  Companies. — Where  the  holding  of  a 
single  grower,  or  the  holding  of  a  company,  is  large,  such  individual  or  company 
has  its  own  fumigating  outfit,  and  the  work  is  in  charge  of  an  employee  who 
understands  the  process.  Sometimes,  also,  two  or  more  neighbors  may  very 
profitably  go  in  together  in  securing  the  equipment  and  do  their  own  work. 


Fig.  1. — Beginning  to  pull  the  tent  over  the  tree. 


Tenting  Material. — At  the  present  time  there  are  three  chief  grades 
of  tenting  material  on  the  market  for  fumigation  work.  These  are 
the  8-ounce  special  army  duck,  the  8-ounce  double-filled  duck,  and  the 
6V2-ounce  drill.  The  first  of  these  materials  is  by  far  the  tightest 
cloth  and  is  the  most  desirable.  The  other  two  allow  about  the  same 
amount  of  leakage  of  gas,  the  duck  being  heavier  and  more  substantial 
than  the  drill.  The  tenting  material  now  in  general  use  consists  almost 
entirely  of    the  8-ounce  double-filled  duck  and  the  G^-ounce  drill. 


The  two  points  to  consider  in  the  purchasing  of  tents  is,  closeness  of 
weave  and  durability.  The  term  "double-filled  duck"  is  somewhat 
misleading  because  it  is  double-filled  in  one  direction  only,  while  the 
special  army  duck  is  double-filled  in  both  warp  and  woof. 

Fumigation  tents  may  be  purchased  from  the  dealers  in  Los 
Angeles,  properly  marked  and  in  any  size  desired.  The  commonest  sizes 
are  from  36  to  45-foot  sizes,  with  larger  ones  up  to  84-foot  tents  for 
large  seedling  trees.  The  size  of  the  larger  trees  will  determine  the 
size  of  the  tents  to  purchase.  If  there  are  but  a  few  trees  that  are 
very  much  larger  than  the  others,  then  two  or  three  larger  sized  tents 
are  desirable.     The  cost  of  a  45-foot  tent  will  range  between  $35  and 


Fig.  2. — A  row  of  tented  trees  as  they  appear  at  night,  when  the 
fumigation  operation  is  carried  on. 


$50,  according  to  the  grade  of  cloth.    The  number  of  tents  to  an  outfit 
is  about  thirty,  although  double  that  number  is  often  used. 

Poles  and  Derricks. — Excepting  with  the  very  large  sized  tents, 
poles  are  used  in  lifting  the  tents  over  the  tree.  These  are  from 
2  to  2y2  inches  in  diameter,  and  should  be  of  straight-grained  pine. 
The  length  of  the  poles  is  usually  14  or  16  feet.  A  half-inch  rope  is 
stapled  about  6  inches  from  one  end  of  the  pole,  and  is  long  enough 
to  reach  two  or  three  feet  beyond  the  opposite  end.  The  tent  is  secured 
to  the  end  of  the  pole  by  placing  a  fold  over  the  end  of  the  pole  and 
then  working  a  half  hitch  over  the  cloth  with  the  rope.  Where  rings 
are  fastened  to  the  tents  these  are  hooked  over  a  metal  pin  on  the  end 
of  the  pole. 


Chemicals  used  in  Fumigation. — Sodium  cyanide  NaCN  is  now 
exclusively  used  in  fumigation  work  because  of  its  lower  cost  and 
greater  source  of  supply.  Sodium  cyanide  is  now  manufactured  in 
this  country,  while  the  potassium  cyanide,  formerly  used,  came  almost 
entirely  from  Germany. 

The  sodium  cyanide  for  fumigation  work  is  of  129  per  cent  purity.  This 
percentage  of  purity  is  on  the  basis  of  100  per  cent  potassium  cyanide.  A 
pound  of  129  per  -cent  sodium  cyanide  contains  about  one-fourth  more  cyanogen 
and  will  consequently  produce  one-fourth  more  gas  than  a  pound  of  99  per  cent 
potassium  cyanide.  If  100  per  cent  purity  was  on  the  basis  of  the  purity  of 
each  product,  as  should  be  the  case,  instead  of  on  the  basis  of  one  product, 
namely,  potassium  cyanide,  then  100  per  cent  sodium  cyanide  would  contain 
one-fourth  more  cyanogen  and  produce  one-fourth  more  gas  than  100  per  cent 
potassium  cyanide,  pound  for  pound.  Much  of  the  cyanide  now  in  use  for 
generating  the  gas  in  pots  comes  in  the  form  of  egg-like  lumps  and  is  known 
as  cyanegg.  Cyanide  in  this  form  is  more  easily  handled,  and  the  uniform  sized 
lumps  insure  a  uniform  generation  of  the  gas.  The  cost  of  sodium  cyanide  is 
22  to  27  cents  per  pound. 

The  acid  used  in  fumigation  work  is  the  commercial  sulphuric  acid  (H2S04) 
of  66  degrees  Beaume,  or  about  93  per  cent  pure.  The  cost  of  this  product 
is  from  1%  to  2  cents  per  pound. 

In  addition  to  the  acid,  water  is  necessary  for  the  generation  of  hydrocyanic 
acid  gas  from  the  cyanide.  If  acid  is  used  alone  with  cyanide,  the  acid  will 
act  for  a  time  in  generating  the  gas,  but  later  a  coating  of  the  product  from 
this  reaction  will  protect  the  cyanide  not  yet  acted  upon.  One  of  the  purposes 
of  the  water  is  to  dissolve  this  coating  as  it  is  formed,  so  that  the  acid  will 
continue  to  come  in  contact  with,  and  to  act  upon,  the  cyanide.  A  second  use 
of  water  is  in  the  heat  produced  when  the  acid  and  water  are  brought  together, 
thus  hastening  the  generation.  A  third  use  of  the  water  is  that  it  simply 
increases  the  volume  of  liquid,  which  is  important  in  covering  the  cyanide  when 
a  small  dosage  is  used,  and  particularly  in  flat-bottomed  generating  vessels. 
Where  water  alone  is  used,  it  will  dissolve  the  cyanide,  but  there  is  no  chemical 
reaction.     This  fact  is  taken  advantage  of  in  the  generating  machine  on  page  7 

Formula  for  Proportions  of  the  Chemicals. — To  insure  the  proper 
generation,  and  secure  the  maximum  amount  of  gas,  the  cyanide,  acid 
and  water  must  be  used  in  the  proper  proportions.  For  sodium 
cyanide  these  proportions  are  as  follows : 

Formula  for  Generation 

Sodium  cyanide  1  ounce  avoirdupois 

Sulfuric  acid,  66°  Beaume  1*4   fluid  ounces 

Water  2  fluid  ounces 

The  water  is  placed  in  the  generating  jar  first,  then  the  acid,  and  later  the 
cyanide. 


Dosage. — The  dosage  is  based  upon  the  distance  around  and  over 
the  tented  tree.  The  simplest  way  of  calculating  this  dosage,  and 
one  which  seems  to  answer  the  purpose  in  practical  work,  for  average 
sized  trees,  is  to  multiply  the  distance  around  by  the  distance  over  the 
tented  tree,  point  off  two  places  in  the  product,  and  then  reduce  this 
by  one-fourth.  This  will  correspond  to  the  full  schedule,  as  given  on 
page  34,  excepting  that  in  the  case  of  the  very  small  trees  the  dosage 
is  increased,  and  in  the  case  of  very  large  trees,  decreased  from  that 
of  the  above  calculation. 

The  amounts  of  acid  and  water  used  are  according  to  the  formula 
given.     If  a  tree  requires  12  ounces  of  sodium  cyanide,  then  12  plus 


Fig.  3. — A  commissary  cart  pulled  by  a  horse;  a  common  type  in 
use  in  Southern  California. 


one-fourth,  or  15  fluid  ounces  of  acid,  and  twice  12,  or  24  fluid  ounces, 
of  water  will  be  needed.  In  practice,  however,  it  is  not  necessary  to 
make  this  calculation,  for  vessels  are  provided  which  are  properly 
graduated  for  this  formula.  With  these  vessels,  if  a  tree  requires  12 
ounces  of  cyanide,  the  acid  pitcher  is  filled  to  the  12  mark  with  acid, 
and  the  water  pitcher  to  the  12  mark  with  water. 

Leakage  and  Care  of  Tents. — Even  with  the  very  best  tents  kept 
in  the  best  condition,  there  is  a  large  leakage  of  gas,  but  when  the  tents 
become  badly  worn  and  have  numerous  holes  on  account  of  tears  and 
acid  burns,  the  escape  of  gas  is  so  great  as  to  seriously  impair  the 
results.      The  tents  are  required  to   be   inspected   daily,   and  where 


holes  occur,  these  should  be  properly  mended.  In  the  case  of  small 
holes,  the  patch  may  be  stuck  on  by  means  of  sheet  rubber  and  a  hot 
iron,  but  large  holes  are  best  repaired  by  a  tailor's  sewing  machine. 
The  advantage  of  the  machine  over  hand-sewing  is  not  that  it  will  be 
better  done  but  the  double  thread  of  the  machine  does  not  leave  the 
holes  that  the  single-thread  hand  sewing  does. 

Practice. — A  fumigating  outfit  consists  of  approximately  thirty 
tents.  More  are  often  handled  in  the  case  of  small  trees,  and  fewer, 
if  the  trees  are  very  large.  Thirty-three  or  four  earthenware  gener- 
ating pots  and  a  commissary  cart  or  tray,  with  minor  appurtenances, 
such  as  scales,  measuring  vessels,  rubber  gloves,  etc.,  are  necessary. 
The  crew  required  to  operate  the  outfit  consists  of  five  men:  two  to 
pull  the  tents,  one  to  measure  the  tented  tree,  kick  in  the  tent,  and 
indicate  the  dosage,  and  two  to  attend  to  the  commissary  and  do  the 
generating.  Sometimes  but  four  men  are  used.  Where  the  portable 
generator,  figure  4,  is  used,  this  number  is  sufficient.  Such  a  crew 
and  outfit  will  treat  about  400  trees  a  night.  The  cost  of  fumigating 
varies  from  20  cents  to  $1.50  per  tree,  with  an  average  cost  of  between 
25  and  30  cents. 

When  the  tent  is  placed  on  the  tree  by  the  tent  pullers,  the  dosage 
man  goes  around  the  tree  and  kicks  in  the  tent,  at  the  same  time 
reading  the  distance  over  and  measuring  the  distance  around  by  means 
of  a  tape  which  he  has  secured  to  the  tent  at  the  starting  point.  The 
cyanide  man  weighs  out  the  amount  of  cyanide  indicated,  while  the 
other  man  measures  out  the  corresponding  amounts  of  acid  and  water, 
and  places  them  in  the  generating  jar.  He  then  carries  this  gener- 
ating vessel  and  also  the  cyanide  to  the  tent  under  which  the  charge  is 
set,  while  the  tent  is  held  up  by  the  other  man.  The  man  handling  the 
acid  is  not  permitted  to  touch  the  tent  at  any  time.  The  acid,  cyanide, 
water,  scales,  etc.,  are  conveniently  arranged  on  a  cart  (see  fig.  3),  or 
on  a  four-legged  tray  which  is  carried  from  tree  to  tree. 

Generating  Machine. — A  machine  for  generating  the  gas  is  now  on 
the  market,  which  gives  promise  of  coming  into  wider  use.  This 
machine  consists  of  a  central  barrel-like  drum  which  encloses  a  smaller 
vessel  in  which  the  generation  of  gas  takes  place.  On  one  side  and 
above  is  a  vessel  containing  the  cyanide  which  is  dissolved  in  the 
required  amount  of  water.  On  the  other  side  is  another  vessel  which 
contains  the  acid.  The  cyanide  in  solution  and  the  acid  are  conducted 
into  separate  graduated  glass  cylinders  for  the  dosage  and  then  turned 
together  into  the  generating  vessel.  As  this  is  within  a  larger  vessel, 
the  only  outlet  is  through  a  rubber  tube,  which  conducts  the  gas  under 


the  tented  tree.*  Only  a  minute  or  two  is  required  for  the  generation. 
Some  advantages  of  such  a  machine  are :  accuracy  of  dosage ;  economy 
of  material ;  cleanliness  of  manipulation ;  one  less  man  required  in  the 
crew;  and  freedom  from  acid  burns  on  the  tents. 

Time  of  Exposure. — Forty-five  minutes  to  one  hour  is  the  usual 
time  the  tents  are  left  on  the  trees.     This  is  about  the  time  required 


Fig.  4. — A  portable  machine  for  generating  hydrocyanic  acid  gas. 


for  the  pulling  of  a  set  of  tents  and  making  the  changes.  At  the  end 
of  this  period,  the  first  tent  is  pulled  on  to  the  tree  in  the  adjoining 
row,  and  so  on  through  the  set. 

Season. — The  season  for  fumigating  extends  approximately  from 
July  15  to  January  1.  Fumigating  earlier  than  the  middle  of  July  is 
not  advisable  because  of  the  danger  of  injuring  the  young  fruit.    Even 


*  A  new  generating  machine  of  different  construction,  and  working  on  some- 
what different  principles,  is  being  placed  on  the  market  for  this  [1915]  season's 
work.     (See  fig.  5.) 


8 


this  date  is  too  early  to  fumigate  for  the  black  scale  because  it  may 
not  be  the  end  of  the  hatching  period.  During  most  seasons  it  will 
be  the  middle  of  August  or  the  first  of  September  before  all  of  the 
black  scale  will  have  hatched.  For  the  citricola  scale  (Coccus  citri- 
cola),  fumigation  should  begin  by  July  15  or  as  soon  thereafter  as 
possible.  This  scale  is  most  susceptible  to  treatment  early  in  the  season 
and  so  far  as  our  present  experience  indicates,  becomes  very  resistant 
after  the  first  or  middle  of  September. 

Temperature. — Fumigation  at  too  low  or  too  high  temperatures 
is  likely  to  cause  injury  to  the  tree,  and  35  degrees  F  has  been  set  for 


^^  ^ ..  i  hi  in  km  i  mini i  ' " 

Fig.  5. — The  cyanofumer,  an  improved  portable  generator. 


the  minimum  and  70  degrees  for  the  maximum  in  Southern  California. 
Experience  during  the  present  season  in  Tulare  County,  however, 
shows  that  fumigation  may  be  carried  on  in  that  section  safely  at  a 
temperature  of  80  to  85  degrees. 

Wind. — Fumigation  should  not  be  carried  on  during  a  high  wind, 
that  is,  wind  enough  to  sway  the  tents.  Neither  is  it  advisable  to  fumi- 
gate in  Southern  California  during  those  occasional  periods  when  the 
atmosphere  is  spoken  of  as  charged  with  electricity.  Judging  from 
the  immunity  of  the  trees  which  were  fumigated  at  high  temperatures 


9 


in  Tulare  County,  this  atmospheric  condition  appears  to  be  a  more 
important  factor  in  burning  than  the  high  temperatures  alone. 

Fumigation  is  practiced  for  the  control  of  the  black,  the  red,  the 
yellow,  the  purple,  and  the  citricola  scales,  and  in  some  cases  possibly 
for  the  mealy  bug.     See  also  under  discussion  of  each  species. 


Fig. 


-Oranges  spotted  by  fumigation. 


SPRAYING  FOR  SCALE  INSECTS  AND  MEALY  BUGS 

On  account  of  the  complaints  that  fumigation  has  not  controlled 
the  black  scale,  and  in  some  cases  also  the  red  and  the  purple  scales ; 
and  because  of  the  expense  involved,  a  very  considerable  interest  in 
spraying  has  been  revived  during  the  past  year  or  two.  There  has 
been,  in  our  opinion,  too  much  of  a  tendency  to  substitute  spraying 


10 


for  fumigation.  As  has  happened  before,  as  soon  as  growers  are  con- 
vinced through  their  own  experience  of  unsatisfactory  results,  this 
method  of  control  will  again  be  on  the  decline. 

The  dense  foliage  of  the  citrus  tree  makes  it  particularly  suitable 
for  fumigating,  while  the  dense  foliage,  together  with  the  fact  that  the 
citrus  tree  is  evergreen,  makes  it  particularly  unsuitable  for  spraying. 
It  is  not  permissible  to  use  a  spray  of  sufficient  concentration  to  kill 
all  of  the  stages  of  scale  insects  on  citrus  trees  because  of  danger  of 
injury.     The  black  scale  may  at  the  proper  stage  be  killed  when  the 


Fig.  7. — Spraying  orange  trees  for  scale  insects. 


spray  strikes  them,  but  the  great  difficulty  in  spraying  citrus  trees  is 
to  hit  all,  or  even  a  sufficient  number,  of  the  scales  to  insure  clean  trees 
and  fruit  the  following  year.  Herein  lies  the  objection  to  and  failure 
of  spraying. 

So  long  as  there  are  even  a  few  scattering  scales  on  the  trees  there 
is  sure  to  be  more  or  less  of  the  sooty  mold  fungus,  which  is  so  seriously 
objected  to  at  the  packing-house,  and  in  the  best  of  spraying  work 
a  few  scales  will  always  be  left.  Two  applications  of  spray  in  a  season 
are  considered  necessary,  and  when  this  is  done,  the  cost  about  equals 
the  cost  of  one  fumigation.  Moreover,  the  same  spraying  program 
will  need  to  be  repeated  year  after  year.     Fumigation,  on  the  other 


11 

hand,  if  at  all  satisfactory,  should  not  require  repeating  for  two  years 
at  least. 

We  are  aware  of  the  fact,  however,  that  in  many  instances  fumi- 
gation has  been  carried  on  year  after  year,  and  still  the  trees  and 
fruit  are  covered  with  the  sooty  mold  fungus.  Similar  conditions, 
though  much  less  frequent,  have  also  occurred  in  the  case  of  the  red 
and  purple  scales.  As  stated  under  "Fumigation,"  we  believe  the 
uneven  hatch  has  been  chiefly  responsible  for  poor  work  in  fumigating 
for  the  black  scale.  In  such  cases,  when  fumigation  has  consistently 
failed  to  control  the  scale,  then  the  grower  is  warranted  in  at  least 


Fig.  8.— A  well 


equipped  supply  wagon  for  carrying  water  and  the  spray- 
materials  to  the  spray  outfits  in  the  field. 


trying  something  else,  and  after  fumigation,  spraying  is  the  next  best, 
in  fact,  the  only  other  means  of  artificial  control. 

While  spraying  should  rarely  if  ever  replace  fumigation  as  a  means 
of  controlling  any  kind  of  scale  insects  in  commercial  orchards,  there 
is  still  a  field  for  spraying  in  the  case  of  young  trees,  or  trees  about 
dooryards,  where  fumigation  may  not  be  convenient,  or  where  the 
infestation  is  light  or  limited  to  occasional  trees. 

Tn  the  case  of  the  mealy  bug  and  the  red  spider,  spraying  is  more 
satisfactory  than  fumigation. 

Materials. — Many  kinds  of  spraying  materials  have  been  developed 
in  response  to  the  recent  increased  interest  in  spraying.     Thus  far, 


12 

however,  all  sprays  which  have  any  established  recognition  for  scale 
insects  on  citrus  trees  consist  of  either  oil  or  soap  or  varying  combi- 
nations. Lime-sulfur  might  be  added  to  the  above,  since  it  has  some 
slight  value  against  the  red  and  the  yellow  scales.  It  requires  a 
rather  strong  spray  to  kill  scale  insects ;  hence  such  neutral  materials 
as  tobacco  or  dilute  soap  which  are  used  successfully  against  such  pests 
as  plant-lice  will  not  kill  the  more  resistant  scales. 

The  number  of  materials  available  for  scale  spraying  is  very  small, 
when  their  killing  power  and  cost  is  considered,  and  there  is  little 
merit  in  many  of  the  numerous  commercial  compounds  that  appear 
periodically  as  panaceas  for  insect  control.  Some  of  these  may  kill 
the  scales  as  well  as  the  standard  sprays,  but  many  of  them  are  likely 
to  do  injury  to  the  citrus  tree. 

On  account  of  the  fact  that  the  black  and  citricola  scales  are  un- 
armored,  the  spray  will  come  in  direct  contact  with  the  insects.  For 
this  reason  spraying  will  come  nearer  being  a  success  with  these  two 
than  with  others.  Red,  yellow,  and  purple  scales  are  armored  scales, 
the  scale  covering  protecting  them  from  direct  contact  with  the  spray. 
With  these  scales,  therefore,  very  poor  results  may  be  expected,  since 
a  spray  strong  enough  to  kill  them  cannot  be  used  on  the  citrus  tree 
without  injury. 

Water  White  Oil,  or  Kerosene  Spray. — Of  all  the  different  mater- 
ials that  have  been  tried,  and  on  which  observations  have  been  made, 
the  kerosene  or  kerosene  emulsion  has  been  the  most  satisfactory.  In 
the  case  of  young  trees,  however,  if  much  of  the  spray  is  allowed  to 
run  down  the  tree  trunk,  injury  is  likely  to  occur  just  beneath  the 
surface  of  the  ground.  Trees  that  are  growing  in  sandy  soil  are  more 
likely  to  suffer  from  such  injury  than  trees  growing  in  heavy  soils. 
The  absorption  is  less  in  sandy  soils,  and  thus  more  of  the  free  kero- 
sene is  left  about  the  tree  trunk,  causing  jury  to  the  bark  and  often 
girdling  the  tree  beneath  the  surface. 

Where  much  kerosene  is  allowed  to  run  down  the  tree  trunk  the 
precaution  should  be  taken  to  remove  the  soil  immediately  around  the 
tree  trunk  as  soon  after  spraying  as  possible,  or  at  least  by  the  follow- 
ing day,  and  replace  this  oil-saturated  soil  with  fresh  soil.  In  the 
case  of  young  trees  without  fruit,  the  distillate  spray,  discussed  in  the 
following  pages,  is  satisfactory  to  use.  Practically  no  injury  results 
to  the  tree  beneath  the  surface  when  distillate  is  used.  If  large 
amounts  of  any  oil  are  allowed  to  run  down  the  tree  it  may  result  in 
injury,  but  there  is  no  excuse  for  allowing  this  waste  to  occur. 

In  the  coast  sections  there  is  usually  little  injury  done  to  the  fruit 
or  foliage  with  the  distillate  spray,  but  in  the  interior  sections  and 


13 

elsewhere,  where  injury  may  occur  to  the  fruit  or  foliage,  the  kerosene 
spray  is  the  safest  to  use. 

"W.  W.,"  or  "Water  White,"  is  the  trade  name  of  what  is  simply 
a  low  grade  of  kerosene,  and  is  the  kind  used  for  spraying  citrus  trees. 
The  cost  in  Los  Angeles  of  the  "W.  W. "  oil  is  7  cents  per  gallon. 


Formula  for  Kerosene  Emulsion 

"  W.  W. "  oil  15  gallons 

Liquid  soap  %  gallon 

or 

Hard  soap  4  pounds 

Water  200  gallons 

If  liquid  soap  is  available,  it  is  preferable  to  hard  soap,  since  no  heating 
is  required.  Hard  soap,  preferably  whale-oil,  is  cut  in  thin  slices  and  dissolved 
in  hot  water.  The  soap  is  placed  directly  in  the  spray  tank  with  10  or  15 
gallons,  or  more  (the  exact  amount  is  not  important)  of  water,  and  then  the 
engine  is  started.  The  oil  is  now  added  slowly,  and  the  materials  are  emulsified 
by  being  run  through  the  pump  under  pressure.  After  a  few  minutes  the  rest 
of  the  water  may  be  added,  and  the  spray  is  ready  to  apply  to  the  trees. 

Distillate  Spray. — In  former  years  distillate  spraying  was  very 
generally  practiced  in  the  orange  groves  of  Southern  California. 
However,  because  of  the  better  results  secured  from  fumigation,  and 
because  of  the  injury  to  the  tree  and  fruit  by  the  distillate  spray,  such 
treatment  went  very  largely  out  of  favor,  though  there  is  still  more 
or  less  distillate  used.  The  old  distillate  was  a  28  degree  gravity 
product,  while  the  tree  distillate  that  is  now  in  use  has  been  addi- 
tionally refined  and  is  of  about  31  degrees  gravity.  This  latter  oil 
is  not  so  likely  to  cause  injury  as  the  old  oil,  but  it  is  more  injurious 
than  kerosene.  This  oil  is  used  at  a  strength  of  2  to  3  per  cent,  while 
the  kerosene  is  used  at  a  strength  of  from  7%  to  10  per  cent.  Because 
of  the  greater  dilution  and  also  the  lower  cost  per  gallon,  the  distillate 
is  much  cheaper.  The  price  of  tree  distillate  in  Los  Angeles  is  five 
cents  per  gallon. 


Formula  for  Distillate  Emulsion 

Tree  distillate  31  °-32°  4  gallons 

Liquid  soap  %  gallon 

or 

Hard  soap  5  pounds 

Water  200  gallons 


14 

These  materials  are  emulsified  in  the  same  manner  as  explained  for  the 
kerosene  emulsion  on  page  13.  If  the  distillate  is  used  without  soap,  the  following 
is  the  formula: 

Formula  for  Straight  Distillate 

Tree  distillate  31°-32°  4  to  6  gallons 

Water 200  gallons 

In  the  case  of  straight  distillate,  the  oil  is  kept  in  suspension  in  the  water  by 
agitation  and  forms  simply  a  mechanical  mixture. 


The  distillate  or  distillate  emulsion  has  been  used  in  the  cooler 
sections  near  the  coast  during  the  past  few  years  with  very  little 
injury  to  the  trees,  but  in  the  interior  sections  where  the  temperature 
is  higher,  there  have  been  more  complaints  of  the  spray  spotting  the 
fruit.  Hot  weather  and  especially  "northers"  are  the  most  important 
influences  in  augmenting  oil  injury  on  citrus  fruit.  Such  injury  on 
the  fruit  is  characterized  by  brown  spots,  which  usually  appear  on  the 
surface  most  exposed  to  the  sun.  Defoliation  is  the  usual  kind  of 
injury  to  the  leaves. 

While  the  addition  of  soap  to  the  oil,  as  used  in  the  distillate 
emulsion,  insures  a  better  mixing  of  the  oil  and  water  particles,  and 
consequently  reduces  liability  to  injury,  too  much  soap  should  not  be 
used,  for  the  soap  itself  may  be  responsible  for  the  spotting  of  fruit. 
Soap  spotting  occurs  on  the  under  side  of  the  fruit,  generally  where 
long  contact  with  the  fruit  results  in  the  injury,  while  oil  spotting 
occurs  on  the  upper  side  of  the  fruit  as  a  result  of  quick  evaporation 
or  heat. 

An  additional  oil  spray  that  the  Station  tried  during  the  past  year 
for  the  first  time  on  citrus  trees  is  a  lime-oil  emulsion.  Instead  of 
using  soap  as  the  emulsifier,  ordinary  freshly  slaked  lime  was  used. 
The  purpose  of  using  the  lime  was  to  try  to  overcome  the  possible 
injury  from  the  oil,  and  since  soap,  if  used  too  freely  as  an  emulsifier, 
will  increase  fruit  spotting,  the  lime  was  substituted  for  the  soap. 
A  very  satisfactory  emulsion  was  made  in  this  way.  This  combination 
has  not  been  used  extensively  enough  as  yet  to  allow  of  definite  rec- 
ommendations. Possibly  the  presence  of  lime  on  the  fruit  may  be 
objectionable.  One  of  the  uses  of  the  lime  was  to  employ  it  in  large 
amounts  in  mealy  bug  spraying  to  coat  over  the  egg  masses  and  young. 
From  20  to  40  pounds  to  200  gallons  of  spray  were  used. 

Miscible  Oils. — Miscible  oil  is  a  term  applied  to  an  oil  that  has 
been  so  treated  as  to  mix  readily  with  water.  The  base  of  a  miscible 
oil  is  usually  a  distillate,  and  the  emulsifier  is  some  soap  combination. 


15 

These  oils  are  convenient  to  apply,  since  it  is  only  necessary  to  add 
the  required  amount  of  water.  The  killing  effect  on  the  scales  is  as 
satisfactory  as  that  of  kerosene  or  distillate,  but  the  greatest  objection 
to  some  of  these  oils  is  that  they  are  likely  to  do  more  injury — at 
least  more  than  kerosene. 

Soap  or  Washing  Powders. — Under  this  head  come  such  products 
as  Goldene,  Gold-Dust,  Lighthouse,  Pearline,  Sea-foam,  and  others  that 
have  been  recently  used  more  or  less  for  citrus  spraying.  These 
powders  are  manufactured  for  washing  purposes  and  were  first  used  by 
citrus  growers  for  washing  the  fruit  in  the  packing-house.  Later,  they 
came  to  be  applied  to  the  trees,  and  at  present  large  amounts  are  being 
used  for  spraying  purposes.  These  washing  powders  are  all  of  about 
the  same  composition,  and  contain  from  25  to  30  per  cent  soap  and 
about  50  per  cent  sodium  carbonate.  The  question  has  arisen  con- 
cerning the  desirability  of  applying  sodium  carbonate  (black  alkali). 
This  is  obviously  an  undesirable  product  to  add  to  the  soil,  but  in 
such  amounts  as  it  is  used  in  spraying  it  is  of  no  consequence. 

These  soap  powders  are  used  at  the  rate  of  1  pound  to  5  or  6 
gallons  of  water,  or  from  35  to  40  pounds  per  tank  of  200  gallons. 
The  question  as  to  whether  the  soap  or  the  sodium  carbonate  is  the 
chief  insecticidal  ingredient  of  such  materials  has  not  yet  been  de- 
termined. If  the  soap  is  the  important  part,  then  it  would  appear 
that  is  would  be  economical  to  purchase  soap  of  greater  purity ;  if  the 
causticity  of  the  sodium  carbonate  is  the  important  factor,  this  or 
some  substitute  might  be  used  alone.  It  is,  of  course,  possible  that 
the  combination  of  the  two  ingredients  is  necessary.  These  and  many 
other  questions  about  spraying  are  under  investigation  by  this  station. 

The  use  of  these  soap  powders  has  become  popular,  indeed  much  too 
popular,  considering  their  actual  value.  They  are  easily  applied,  since 
it  is  only  necessary  to  put  the  material  into  the  spray  tank.  They  will 
kill  many  of  the  black  scales  in  their  younger  stages,  as  many  sprays 
will,  but  with  the  more  mature  scales,  washing  powders  are  not  so 
effective  as  the  oil  and  soap  sprays.  The  supposed  lack  of  injury  to 
the  fruit  has  been  an  important  factor  in  their  favor,  but  it  is  now 
very  well  known  that  these  powders  often  cause  spots  on  the  fruit, 
so  that  in  this  regard  they  are  in  the  same  category  as  most  of  the 
other  sprays  discussed. 

Applying  the  Spray. — The  most  important  phase  of  the  whole 
process  of  spraying  a  citrus  tree  is  the  thoroughness  of  application. 
Even  when  the  spray  is  applied  most  thoroughly,  there  will  be  a  good 


16 

many  insects  that  are  not  touched.  This  is  due  to  the  numerous 
leaves  that  are  bound  to  shield  some  parts  from  the  spray.  Since 
the  scales  are  largely  on  the  under  side  of  the  leaves  at  the  time  of 
spraying,  the  "uppershot"  should  be  used  almost  entirely.  By  the 
time  this  spraying  from  below  is  finished,  and  the  excess  spray  falls  on 
the  upper  surfaces,  very  little  direct  "overshot"  work  is  necessary. 

Season  for  Spraying. — Since  spray  work  against  scale  insects  is 
chiefly  valuable  for  the  black  and  citricola  scales,  when  these  insects 
are  young  and  susceptible,  the  season  for  spraying  is  limited.  This 
will  be,  generally  speaking,  from  August  first  to  December  first.  Early 
spraying,  that  is,  just  as  soon  as  all  of  the  insects  have  hatched,  is 
the  most  desirable  time.  If  a  second  application  is  to  be  made,  this 
may  follow  a  few  weeks  later,  but  from  our  work  this  season,  we 
believe  that  more  time  spent  on  a  single  application,  making  a  single 
thorough  job,  is  not  only  more  economical  but  also  more  effective. 

Equipment. — Except  in  the  case  of  small  trees,  or  in  that  of  a  few 
large  trees,  a  power  sprayer  is  necessary  for  citrus  spraying.  With 
a  power  sprayer  a  pressure  of  200  pounds,  or  over,  can  be  maintained 
with  four  nozzles  on  two  leads  of  hose. 

For  scale  insect  spraying,  the  Bean  mist,  Bean  whirlpool,  or 
Friend  Drive  spray  nozzles  are  satisfactory.  Tests  made  with  the 
Bean  Mist  and  Whirlpool  nozzles  showed  that  the  character  of  spray 
from  each  is  about  the  same  and  that  about  the  same  amount  of 
spray  in  a  given  time  is  thrown  by  each.  This  amount  is  1  gallon 
or  a  little  over  per  minute,  per  nozzle,  when  a  pressure  of  200  pounds 
is  maintained.  The  mist  nozzle  throws  the  spray  at  an  angle  of  45 
degrees  from  the  horizontal,  while  with  the  whirlpool,  the  angle  is 
75  to  80  degrees.  The  45  degree  angle  is  preferable,  because  it  enables 
better  "undershot"  work  to  be  done.  Tests  made  with  the  Bordeaux 
type  of  nozzle,  such  as  the  Bean  Clipper,  showed  that  the  amount  given 
off  by  each  nozzle  when  a  pressure  of  200  pounds  was  maintained  was 
1.7  gallons  per  minute. 

When  spraying  for  mealy  bugs,  it  is  very  important  to  use  much 
force  with  the  spray  so  that  it  will  penetrate  the  egg  masses  and  the 
cottony  covering  of  the  insects  themselves.  This  cannot  be  done  to 
the  best  advantage  with  the  ordinary  type  of  nozzle;  but  the  M.  A.  C. 
nozzle  answers  this  requirement  very  well.  In  order  to  get  pressure, 
it  is  necessary  to  throw  a  large  volume  of  spray.  Tests  with  this 
nozzle  showed  that  nearly  5  gallons  per  minute  were  given  off.  Where 
such  large  quantities  are  used,  the  spray  may  be  diluted  more  than 
is  called  for  in  the  regular  formula.  In  fact,  this  nozzle  is  most  satis- 
factory for  applying  pure  water  for  the  mealy  bug.     The  water  is 


17 

applied  with  such  force  that  the  insects  are  dislodged  from  the  tree, 
and  at  the  same  time  many  are  killed.  Reinfestation  from  the  live 
ones  on  the  ground  is  prevented  by  applying  tanglefoot  or  cotton  bands 
to  the  tree  trunks. 

Amount  of  Spray. — The  amount  of  spray  necessary  for  citrus  trees 
depends  on  the  size  of  the  tree  and  upon  how  thoroughly  the  work  is 
done.  For  average  trees  the  amount  will  be  8  to  10  gallons.  Much 
less  will  suffice  for  trees  under  five  or  six  years  old,  but  as  much  as 
15  to  25  gallons  will  be  needed  for  large  Valencias  or  for  seedlings. 


SPRAYING    FOR   RED    SPIDERS    AND    MITES 

Spraying  is  now  very  generally  used  throughout  the  citrus  belt 
for  the  control  of  red  spiders  and  mites.  The  other  means  of  con- 
trolling these  pests  is  by  the  application  of  dry  sulfur.  Dry  sulfur 
is  a  satisfactory  treatment  for  spiders  and  mites,  but  the  results  are 
more  dependent  upon  proper  weather  conditions  than  is  the  case  with 
liquid  sprays.  The  unpleasantness  of  applying  sulfur  in  the  dry  state, 
and  the  fact  that  fruit  pickers  complain  of  the  sulfur  several  weeks 
after  the  application,  have  made  this  method  of  control  much  less 
popular  than  spraying.  Where  dry  sulfur  is  used,  the  addition  of 
hydrated  lime,  in  the  proportion  of  one  part  of  lime  to  two  or  three 
parts  of  sulfur,  is  used  to  increase  the  adhesive  power  and  as  a  diluent. 
The  application  is  best  made  by  means  of  a  power  blower  shown  in 
figure  10.  The  cost  of  applying  dry  sulfur  is  about  one-half  that  of 
spraying. 

In  spraying,  the  essential  ingredient  to  apply  is  sulfur  because 
of  its  prolonged  action.  The  commercial  lime-sulfur  is  now  very 
generally  used  for  spiders  and  mites. 


Lime-sulfur  Spray  for  Spiders  and  Mites 

Commercial  lime-sulfur  4-5  gallons 

Water  200  gallons 

The  lime-sulfur  is  added  directly  to  the  spray  tank,  which  has 
previously  been  filled  with  water,  and  after  a  little  agitation  it  is 
ready  to  apply  to  the  trees.  Some  growers  prefer  to  add  flour  paste", 
which  increases  the  spreading  of  the  spray  and  also  makes  it  stick  to 
the  foliage  better.     The  flour  paste  is  made  by  using  flour  at  the  rate 


18 

of  a  pound  to  a  gallon  of  water  and  bringing  it  to  the  boiling  point. 
From  6  to  8  gallons  of  this  is  used  to  a  200-gallon  tank.  There  is  more 
or  less  trouble  in  making  this  paste,  however,  and  some  growers  prefer 
to  add  the  flour  dry  (6-8  pounds  to  200  gallons)  to  the  spray-tank. 
The  addition  of  flour,  or  flour  paste,  is  not  absolutely  essential  for 
the  control  of  spiders  on  citrus  trees,  and  it  is  often  omitted.  Where 
the  spiders  are  especially  persistent,  as  in  San  Diego  County,  it  is 
desirable  to  add  15  or  20  pounds  of  dry  sulfur  to  the  commercial  lime- 
sulfur  spray. 


am 

W3 


Fig.  9. — Lime-sulfur  injury. 


Time  of  Spraying  for  Spiders  and  Mites, — The  general  rule  is  to 
apply  the  spray  when  the  spiders  first  become  numerous  and  do 
damage.  This  is  usually  in  May,  June,  or  July,  but  during  some  years 
and  in  some  sections  treatment  is  needed  at  other  seasons.  While 
spiders  and  mites  are  widely  distributed  and  may  be  found  to  some 
extent  everywhere,  treatment  is  not  advisable  until  they  are  abundant 
enough  to  do  conspicuous  injury. 


19 

Lime-sulfur  spraying  should  be  avoided  during  very  hot  weather. 
Even  if  hot  weather  follows  several  days  after  the  application  is 
made,  injury  will  result  to  the  fruit  and  foliage.  Lime-sulfur  injury 
(see  fig.  9),  consists  of  brown  and  dried  areas  where  the  fruit  is  ex- 
posed to  the  sun.  Atomic  or  milled  sulfur  and  soluble  sulfur  have 
recently  come  into  use,  and  these  materials  may  cause  less  injury  than 
the  ordinary  lime-sulfur.  The  use  of  atomic  and  milled  sulfur  has 
not  been  extensive  enough,  as  yet,  to  make  possible  definite  statements 
about  their  efficiency  for  spiders  on  citrus  trees. 


Fig.  10. — Applying  dry  sulfur  and  hydrated  lime  for  red  spiders. 


THE   BLACK   SCALE 
(Saissetia  oleae,  Bern.) 

The  black  scale  is  generally  distributed  in  all  of  the  citrus  sec- 
tions south  of  the  Tehachapi,  and  is  the  most  important  citrus  insect 
pest  in  California.  It  is  not  a  pest  in  the  citrus  sections  of  the  San 
Joaquin  or  Sacramento  Valleys,  but  it  sometimes  occurs  abundantly 
on  the  scattering  orange  plantings  in  the  coast  valleys  north  of  the 
Tehachapi.  In  Southern  California  it  occurs  most  abundantly  in 
the  coast  counties,  but  recently  it  has  also  become  entitled  to  first 
place  as  a  pest  in  the  interior  sections,  as  in  Riverside,  for  example. 


20 


The  black  scale  draws  the  sap  from  the  tree  and  injures  the 
smaller  twigs,  and  also  reduces  the  vigor  of  the  tree.  But  probably 
the  most  important  injury  is  due  to  the  sooty  mold  fungus  that  grows 
in  the  honey-dew  given  off  by  the  scale.  This  honey-dew  and  fungus 
interfere  with  the  normal  growth  of  the  tree  and  also  necessitate 
the  washing  of  the  fruit  in  the  packing-house. 

There  is,  as  a  rule,  but  one  generation  of  the  black  scale  in  a 
season.  The  average  number  of  eggs  deposited  is  about  two  thousand. 
The  young  appear  most  abundantly  during  May,  June,  July,  and 
August.     However,  since  some  of  the  scales  may  develop  in  less  than 


Fig.  11. — Black  scale  on  orange  twig. 


a  year,  the  insect  may  be  found  somewhere  in  different  stages  at  all 
seasons.  This  uneven  hatch,  which  is  most  common  near  the  coast, 
is  the  most  important  factor  accounting  for  poor  results  from  fumi- 
gation. It  is  usually  about  September  first  before  all  of  the  scales 
have  hatched,  and  thus  the  fumigation  season  should  begin  for  this 
scale  at  about  this  date.  Some  groves  will  be  found  in  every  district 
in  which  there  is  a  more  complete  hatch  than  in  others,  and,  so  far 
as  possible,  early  fumigation  should  be  done  in  such  groves.  A  75 
per  cent  schedule  (p.  32)  is  satisfactory  for  this  scale  if  the  insects 
are  in  the  proper  stage.  Where  there  are  still  a  few  eggs,  or  scales 
that  are  well  advanced,  a  full  schedule   (p.  34)   is  necessary  if  this 


21 

can  be  used  with  safety  to  the  trees.  In  the  coast  districts,  however, 
there  is  danger  of  doing  too  much  injury  to  the  fruit  with  this  dosage, 
and  thus  a  75  or  85  per  cent  schedule  is  as  high  as  it  is  safe  to  use. 
The  season  for  spraying  and  fumigating  is  about  the  same ;  the  earlier 
the  work  is  done  after  all  the  insects  are  hatched,  the  more  susceptible 
will  be  the  scales. 


THE  RED  AND  YELLOW  SCALES 

(Chrysomplialus  aurantii,  Mask) 

(Chrysompliahis  aurantii  var.  citrinus,  Coq.) 

While  the  red  scale  is  not  so  generally  distributed  as  the  black,  it 
is  nevertheless  found  in  most  of  the  citrus  sections  of  Southern 
California.  It  does  not  occur  in  commercial  plantings  north  of  the 
Tehachapi.  The  yellow  scale  has  much  the  same  distribution  in  the 
south,  but  in  addition  it  occurs  in  the  Sacramento  Valley. 

The  red  scale  attacks  the  branches,  leaves,  and  fruit,  while  the 
yellow  scale  is  but  rarely  found  on  the  twigs  and  branches.  These 
scales  give  off  no  honey-dew  as  is  the  case  with  the  black  scale,  so 
that  the  injury  they  cause  is  due  directly  to  the  feeding  and  the 
presence  of  the  scales  themselves  on  the  fruit. 

There  are  never  any  eggs  present  with  the  red  and  the  yellow  scales, 
since  the  young  are  brought  forth  alive.  This  fact  is  taken  to  account 
for  these  scales  being  susceptible  to  fumigation  at  any  season,  since 
eggs  are  considered  more  difficult  to  kill.  Every  female  may  produce 
one  hundred  young,  and  these  mature  in  three  months.  There  are  thus 
between  three  and  four  generations  in  a  year.  A  single  individual  of 
this  species  produces  much  fewer  young  than  the  black  scale,  but 
because  of  the  greater  number  of  generations,  the  progeny  from  a 
single  red  scale  is  much  greater  at  the  end  of  the  season  than  that  of 
a  black  scale. 

Good  results  from  fumigation  are  usually  considered  easier  to 
obtain  with  the  red  and  the  yellow  scales  than  with  any  of  the  other 
scales,  excepting  the  black  scale  when  it  is  in  the  proper  stage. 
However,  there  are  certain  refractory  cases  where  fumigation,  done 
apparently  in  a  proper  manner,  has  not  been  satisfactory  against  the 
red  scale.  A  75  per  cent  schedule  (p.  32)  is  generally  considered 
sufficient  for  this  scale.  Where  the  results  of  previous  seasons  have 
not  been  satisfactory  and  where  climatic  conditions  will  allow,  the  100 
per  cent  schedule  (p.  34)  may  be  used. 


22 


THE  PURPLE  SCALE 

(Lepidosaphes  becMi,  Newm.) 

The  purple  scale  is  scatteringly  distributed  in  all  of  the  counties 

south  of  the   Tehachapi,   excepting  Riverside,   San   Bernardino,   and 

Imperial.     It  does  not  occur  elsewhere  in  California  in  commercial 

plantings. 

From  forty  to  eighty  eggs  are  deposited  by  this  scale,  and  about 
three  months  are  required  for  the  development  of  the  young.     The 


Fig.  12. — Purple  scale  on  orange  leaf. 


number  of  generations  is  about  the  same  as  that  of  the  red  scale,  or 
between  three  and  four. 

The  purple  scale  attacks  all  parts  of  the  tree,  and  kills  the  smaller 
twigs  and  branches.  No  honey-dew  is  secreted  by  this  species,  and 
consequently  there  is  no  sooty  mold,  but  the  scales  themselves  occur 
on  the  fruit  and  are  difficult  to  remove. 

This  scale  is  particularly  resistant  to  fumigation.  This  is  due  to 
the  fact  that  there  is  scarcely  any  season  when  eggs  may  not  be  found 
beneath  the  scale  covering,  and  these  are  difficult  to  kill.  For  this 
reason  the  heaviest  schedule  of  dosage  should  be  used  that  is  consistent 
with  safety  to  the  trees  in  the  different  sections.     The  100  per  cent 


23 

schedule  (p.  34)  should  be  used  wherever  possible.  In  the  coast  dis- 
tricts, where  this  is  not  desirable,  an  85  per  cent  schedule  (p.  33) 
may  be  employed. 

THE  CITRICOLA  SCALE 
(Coccus  citricola,  Campb.) 

The  citricola  scale  is  a  very  recent  citrus  pest  in  California,  and 
is  one  of  considerable  importance.  It  occurs  in  Riverside,  San  Ber- 
nardino, and  Orange  counties,  in  Southern  California,  and  also  in 
many  of  the  citrus  sections  of  the  San  Joaquin  and  the  Sacramento 
valleys. 

The  young  of  this  scale  appear  mostly  in  May,  June,  and  July, 
with  some  extension  at  both  ends  of  this  period.  The  young  occur 
mostly  on  the  leaves  until  spring,  when  they  move  back  to  the  twigs. 
Approximately  one  year  is  required  for  their  development,  and  thus 
there  is  but  one  generation  in  a  season.  The  injury  is  due  to  the 
feeding  of  the  insects,  and  also  to  the  sooty  mold  and  the  honey-dew, 
which  impairs  the  health  of  the  tree  and  makes  washing  of  the  fruit 
necessary. 

The  citricola  scale  becomes  very  resistant  to  fumigation  after  early 
in  September.  The  fumigation  season,  when  entirely  satisfactory 
results  may  be  secured,  is  therefore  very  short  with  this  scale.  From 
July  15  to  September  15  is  the  best  season.  A  75  per  cent  schedule 
(p.  32)  has  often  given  satisfactory  results  against  this  scale,  but  in 
other  cases  live  scales  may  be  found  with  this  dosage.  In  the  interior 
sections,  where  it  can  be  used  safely,  a  100  per  cent  schedule  is  more 
certain.  In  the  coast  districts  an  85  per  cent  schedule  (p.  33)  may 
be  substituted.  In  the  San  Joaquin  citrus  sections,  a  110  per  cent 
schedule  ought  to  be  employed,  at  least  after  the  first  two  or  three 
weeks  of  the  season. 

For  spraying  for  this  scale  see  under  general  head  of  spraying  on 
page  9.  The  season  is  about  the  same  as  the  fumigating  season,  though 
it  may  be  prolonged  until  after  September  15. 

OTHER  LESS  IMPORTANT  SCALE  INSECTS 

The  Soft  Brown  Scale  (Coccus  hesperidum)  always  appears  in 
isolated  cases  on  small  trees  or  on  a  few  twigs  of  old  trees,  but  usually 
disappears  before  treatment  is  necessary.  This  species  is  very  similar 
to  the  citricola  scale,  but  the  massing  of  the  scales  on  but  a  portion 
of  the  tree  will  usually  distinguish  the  soft  brown  from  the  citricola 
scale,  which  occurs  generally  over  the  entire  tree.  The  citricola  scale 
when  mature  is  also  of  a  grayer  color  and  is  rarely  found  on  the 


24 


leaves;  while  the  mature  soft  brown  scales  are  very  likely  to  occur  on 
the  under  side  of  the  leaves. 

The  Greedy  Scale  (Aspidiotus  rapax,  Comst.)  and  the  Oleander 
Scale  (Aspidiotus  hederae,  Comst.)  are  circular  gray  scales  that  some- 
times occur  on  citrus  trees,  and  particularly  on  the  old  mature  fruit. 
Their  occurrence  and  injury,  however,  is  not  important  enough  to  make 
control  measures  necessary,  except  in  rare  cases. 

The  Cottony  Cushion  Scale  (leery a  purchasi,  Mask.)  may  also 
occur  in  sporadic  cases  in  commercial  citrus  planting,  but  as  a  rule  the 


Fig.  13. — The  Citricola  scale. 

infestation  is  not  permanent  enough  to  require  any  treatment.  Where 
the  scales  do  not  disappear  in  a  reasonable  time,  a  quantity  of  them 
should  be  collected  and  sent  to  the  State  Insectary,  at  Sacramento, 
with  a  request  for  a  colony  of  beetles. 


CITRUS  MEALY  BUGS 
There  are  three  or  four  different  mealy  bugs  that  attack  citrus  trees. 
The  most  imprtant  one  and  the  one  most  widely  distributed  is  the 
citrus  mealy  bug  (V suedococcus  citri) .     This  is  a  very  important  pest 


.25 

that  does  injury  by  taking  the  nourishment  from  the  tree,  and  also 
excreting  honey-dew,  in  which  the  sooty  mold  fungus  gro.ws.  Masses 
of  eggs  and  the  insects  themselves  may  also  occur  on  the  fruit,  and 
are  particularly  difficult  to  remove  when  they  secrete  themselves  in 
the  navel  of  the  orange  as  they  often  do. 

The  eggs  are  laid  in  cottony  masses  to  the  number  of  300  or  500. 
and  the  development  of  the  young  requires  from  one  and  a  half  to 
three  months,  according  to  the  season.  They  are  more  or  less  dormant 
during  the  winter  and  are  not  seen  in  large  numbers  on  the  trees  at 
this  season,  but  with  the  appearance  of  warm  weather  in  the  spring 
and  summer,  they  rapidly  appear  and  reinfest  the  tree.  Infestations 
of  the  mealy  bug  appear  from  time  to  time  on  a  few  trees  and  after- 
ward disappear  even  though  no  control  measures  are  employed.  In 
other  cases,  however,  infestations  will  persist  for  several  years,  and 
control  measures  are  very  necessary. 

The  distribution  of  the  citrus  meaty  bug  is  general  over  the  state, 
but  it  has  not  appeared  as  a  pest,  as  yet,  in  the  citrus  groves  of 
Riverside  and  San  Bernardino  counties  in  Southern  California  or  in 
the  San  Joaquin  section. 

Mealy  bugs  are  the  most  difficult  to  control  of  all  the  citrus  insects. 
This  is  because  they  are  almost  wholly  resistant  to  fumigation  as 
ordinarily  practiced,  and  because  they  are  also  very  resistant  to  sprays. 
Their  resistance  to  sprays  is  due  to  the  large  amount  of  cottony  secre- 
tion protecting  both  the  insects  and  eggs  from  the  spray  material. 

However,  of  the  available  methods,  spraying  is  the  most  satis- 
factory. Much  force  is  important  in  applying  the  spray  to  these 
insects.  None  of  the  composition  sprays  that  have  yet  been  tried  are 
better  than  kerosene  emulsion,  or  distillate  emulsion,  but  spraying 
for  the  mealy  bug  should  be  repeated  frequently,  about  three  applica- 
tions in  a  season.  Spraying  with  pure  water  and  the  use  of  the 
M.  A.  C.  nozzles  has  also  given  satisfactory  results  (see  p.  16). 

RED  SPIDERS  AND  MITES 
Next  to  the  scale  insects  and  mealy  bugs,  red  spiders  and  mites  are 
the  most  troublesome  pests  on  citrus  trees.  There  are  three  species 
of  importance:  the  citrus  red  spider  (Tetranychus  mytilaspides) ,  the 
six-spotted  mite  (Tetranychus  sexmaculatus) ,  and  the  silver  mite 
(Eriophyes  oleivorus) .  The  citrus  red  spider  is  very  generally  dis- 
tributed and  is  responsible  for  the  most  injury.  The  six-spotted  mite 
is  more  restricted  to  the  coast  districts  and  is  probably  most  important 
in  San  Diego  County.  The  silver  mite  is  limited  to  a  portion  of  San 
Diego  County  only. 


26 

Red  spiders  and  mites  cause  the  pale  silver  color  on  the  leaves  and 
fruit  by  withdrawing  the  plant  juices.  In  cases  of  severe  attack, 
leaves  so  damaged  fall  from  the  tree. 

The  two  common  species  of  red  spiders  attacking  citrus  trees  have 
about  the  same  life  cycle.  About  thirty  eggs  are  deposited,  which 
hatch  in  eight  to  ten  days,  and  twelve  days  more  are  required  for  the 
young  to  develop.  The  whole  life  cycle  of  the  red  spider,  from  the 
hatching  of  the  egg  to  the  death  of  the  adult,  occupies  from  thirty 
to  forty  days.  There  are  several  generations  in  a  season,  probably 
twelve  or  fifteen. 

For  the  control  of  red  spiders  and  mites  see  page  17. 


Fig.  14. — Scars  of  thrips  on  orange. 


THRIPS 

(Euthrips  citri,  Moul.) 

Thrips  occur  most  abundantly  in  Tulare  County.  In  Southern 
California,  occasional  injury  from  thrips  occurs  in  the  vicinity  of 
Redlands  and  Riverside.  The  thrips  do  injury  to  orange  trees  by 
causing  a  leathery  distorted  growth  of  the  leaves,  and  a  scarred  ring 
about  the  stem  end,  and  other  less  sharply  denned  scars  on  other  parts 
of  the  fruit.  Spraying  was  carried  on  in  many  groves  in  Tulare  in 
1910,  but  the  results  scarcely  justified  the  expense  of  the  three,  or  even 
four  sprayings  that  were  necessary,  and  since  that  time  practically 
no  spraying  for  thrips  has  been  done.  The  extent  of  injury  during 
recent  years  has  not  been  so  groat  in  that  section,  and  it  is  no  longer 
considered  profitable  to  spray  for  this  insect. 


27 


Thrips  appear  in  the  early  spring,  about  April  15,  and  there  is 
a  succession  of  broods  until  November.  About  twenty  days  are 
required  for  their  development,  and  the  average  life  of  the  adult  is 
about  twenty-five  days.  Pupation  does  not  necessarily  occur  in  the 
ground  but  in  old  leaves,  rubbish,  and  in  blossoms. 

THE  ORANGE  TORTRIX 

(Tortrix  citrana,  Fern.) 

The  larva  of  this  insect,  which  is  about  one-half  inch  long,  bores 
into  the  fruit,  though  going  no  deeper  than  just  through  the  rind. 
Fruit  with  such  burrows  is  classed  as  culls,  not  only  because  of  the 


Fig.  15. — Showing  the  character  of  burrows  in  the  orange  rind 
made  by  the  orange  tortrix. 

burrow  itself,  but  because  decay  infection  usually  results  therefrom. 
Many  such  fruits  fall  from  the  tree. 

While  in  some  limited  sections  in  the  early  part  of  the  shipping 
season,  as  much  as  5  per  cent  of  the  fruit  may  be  attacked  by  this 
insect,  the  damage  has  never  been  considered  sufficient  to  warrant 
practicing  any  control  measure. 


FULLER'S  ROSE  BEETLE 
(Aramigus  fulleri,  Horn.) 

Fuller's  rose  beetle  is  a  grayish  brown  beetle  that  measures  a  little 
more  than  a  quarter  of  an  inch  in  length.  This  beetle  may  be  seen 
clinging  to  a  twig,  the  under  side  of  a  leaf,  or  at  the  forks  of  the 
smaller  branches,  during  the  day.    It  feeds  at  night. 


28 

The  injury  (see  fig.  16)  is  never  of  any  consequence  on  old  trees, 
but  on  young  or  budded  trees,  all  of  the  tender  growth  may  be 
attacked.  On  such  trees  protection  is  afforded  by  first  jarring  off  the 
beetles  onto  the  ground,  and  applying  a  cotton  band  to  prevent  their 


Fig.  16. — Work  of  Fuller's  rose  beetle  on  orange  leaves. 


re-ascent.  Not  having  functional  wings,  they  cannot  fly  into  the  trees. 
A  strip  of  ordinary  cotton  batting,  three  or  four  inches  wide,  is  placed 
about  the  tree  trunk  and  tied  with  a  string  around  the  lower  edge 
of  the  band.  The  band  is  then  pulled  down  over  the  string,  thus 
forming  a  barrier  to  the  beetles  that  attempt  to  crawl  up  the  tree  trunk. 


29 

DIABKOTICA 
This  is  a  black  and  green  beetle  that  does  injury  (see  fig.  17) 
somewhat  like  that  of  Fuller's  rose  beetle.  The  tender  growth  on 
young  orange  trees  is  attacked.  Little  or  no  injury  is  done  to  the 
lemon.  Since  these  beetles  fly,  they  cannot  be  controlled  in  the  same 
way  as  Fuller's  rose  beetle.     They  may,  however,  be  jarred  off  the 


Fig.  17. — Work  of  Diabrotica  on  orange  leaves. 

small  trees  onto  a  canvas  in  the  early  morning  before  they  become 
active,  and  then  killed.  If  the  injury  is  extensive  and  severe,  the 
young  growth  of  the  trees  may  be  sprayed  with  arsenate  of  lead, 
using  10  pounds  to  200  gallons  of  water. 


APHIDES  OR  PLANT-LICE 
In  the  early  spring,  some  of  the  tender  shoots  of  citrus  trees  may 
be  thickly  covered  with  plant-lice.     The  result  of  their  injury  is  a 


30 


Fig.  18.— Cast  skins  of  aphides  on  orange  leaves. 


31 

curling  of  the  leaves  and  a  checking  of  growth  of  the  shoot.  Usually 
their  attacks  are  confined  to  a  few  shoots  so  that  their  effect  on  the 
tree  as  a  whole  is  not  often  serious.  They  may  suddenly  disappear, 
too,  in  the  midst  of  a  maximum  infestation,  and  control  work  is  not 
often  necessary.  If  they  persist  and  do  injury  to  young  trees  or 
nursery  stock,  spraying  with  a  soap  solution  (1  pound  to  6  or  8  gallons 
of  water)  will  check  them. 


FUMIGATION  DOSAGE  TABLES 

The  dosage  tables  on  the  following  pages  give  the  amount  of 
cyanide  for  any  sized  tree.  The  75  per  cent  or  85  per  cent  schedules 
are  more  generally  used  in  the  sections  near  the  coast ;  while  the  100 
per  cent  schedule  is  often  used  in  the  interior.  The  110  schedule  has 
been  used  thus  far  mostly  in  Tulare  County. 

To  obtain  the  dose  for  any  given  tree,  find  the  distance  over,  in 
the  column  of  figures  on  the  left  of  the  page ;  continue  in  this  same 
horizontal  column  until  directly  under  the  figure  for  the  distance 
around.  The  number  at  this  point  will  be  the  amount  in  ounces  of 
sodium  cyanide  for  the  given  sized  tree.  To  determine  the  amount 
of  acid,  add  one-fourth,  and  for  the  water  double  the  figure  for  the 
cyanide.  This  calculation  is  not  necessary,  however,  in  practice,  as 
especially  graduated  vessels  are  in  use,  as  explained  on  page  5. 


10 


<D 


32 


75%  SCHEDULE  SODIUM  CYANIDE 

Distance  around,  in  feet 
16  18  20  22  24  26  28  30  32  34  36  38  40  42 


12 

2 

3 

3 

3 

3 

3 

14 

3 

3 

3 

3 

3 

3 

3 

3 

3 

3 

4 

4 

16 

3 

3 

3 

3 

3 

3 

3 

3 

3 

4 

4 

4 

4 

4 

18 

3 

3 

3 

3 

3 

3 

4 

4 

4 

4 

4 

4 

4 

5 

20  22  24  26  28  30  32  34  36  38  40  42  44  46  48  50 


4 

4 

4 

4 

4 

5 

5 

5 

5 

6 

6 

6 

6 

4 

4 

4 

5 

5 

5 

5 

6 

6 

6 

6 

7 

7 

4 

5 

5 

5 

5 

6 

6 

6 

6 

7 

8 

8 

5 

5 

6 

6 

6 

6 

7 

7 

8 

8 

8 

20 
22 
24 
26 
28 


30  32  34  36  38  40  42  44  46  48  50  52  54  56  58  60  62  64 

30   5  6   6   6   7  7  8  8  8  8  8  8  9  10  11  11  11  11 

32  7   8  8  8  8  9  9  9  10  10  11  11  11  11  12 

34  8  8  9  10  10  11  11  11  11  12  12  13  13  13 

36  8  8  9  10  10  11  11  11  11  12  12  13  13  13 

38  9  9  10  11  11  11  12  12  13  13  13  14  14 


42  44  46  48  50  52  54  56  58  60  62  64  66  68 

|  40  10  11  11  11  11  12  13  13  14  14  14  15  15  15 

S  41  11  11  11  11  12  13  13  14  14  14  15  15  15  16 

42  11  11  12  13  13  14  14  14  15  15  15  16  16 

43  12  13  13  14  14  14  15  15  15  15  16  17 

44  13  14  14  14  15  15  15  16  17  17 


50  52  54  56  58  60  62  64  66  68 

45  13  14  14  15  15  15  16  17  17  17 

46  14  14  15  15  15  16  17  17  17  17 

47  14  14  15  15  16  17  17  17  17  18 

48  14  15  15  16  17  17  17  17  18  18 

49  14  15  16  16  17  17  17  17  18  19 


60  62  64  66  68  70  72  74  76 

50  17  17  18  18  19  19  20  21  21 

51  18  18  19  20  20  21  21  21 

52  19  19  20  21  21  22  23 

53  20  20  21  22  23  24 

54  21  21  22  23  24 


33 


85%  SCHEDULE  SODIUM  CYANIDE 

Distance  around,  in  feet 
16     18     20     22     24     26     28     30     32     31     36     38     40     42 
10       2       3       3       3       3 
12       2       3       3       3       3       3 

14       33333344444       5 
16       33       3       34444455555 
18       3334445       5       555       5       55 

20  22     24     26     28     30     32     34     36     38     40     42     44     46     48     50 

20                        3  4       4       5       5       5       5       5       5       5       5       5       6       6       7       7 

22  55555555667777 

2i  5555556777788 

26  5       5       5667777899 

28  567777889     10     10 


30  32  34  36  38  40  42  44  46  48  50  52  54  56  58  60  62  64 

30   6   7   7   7   8   8  9  9  10  10  10  10  11  12  13  13  13  13 

8   9   9  10  10  11  11  11  12  12  13  13  13  13  14 

9  10  10  11  12  12  13  13  13  13  13  14  14  15 

10  10  11  12  12  13  13  13  13  14  15  15  15  15 

11  11  12  13  13  13  14  14  15  15  15  15  15 


40  42  44  46  48  50  52  54  56  58  60  62  64  66  68 

|  40  11  12  13  13  13  13  14  15  15  15  15  16  17  17  17 

S  41  13  13  13  13  14  15  15  15  15 

42  13  13  14  15  15  15  16  16 

43  14  15  15  15  16  16  17 

44  15  15  16  16  17  17  17  18  19  19 


50  52  54  56  58  60  62  64  66  68 

45  15  15  16  17  17  17  18  18  20  20 

46  15  16  17  17  17  18  19  19  20  20 

47  15  16  17  17  18  19  19  20  20  21 

48  16  17  17  18  19  19  20  20  21  21 

49  16  17  18  18  19  20  20  20  21  22 


60  62  64  66  68  70  72  74  76  78 

50  20  20  21  22  22  22  23  24  24  24 

51  21   22  22  22  23  24  24  24  25 

52  22  22  23  24  24  24  25  26 

53  22  23  24  24  25  26  27 

54  24  24  25  26  27  28 


--H 

32 
34 

_3 

36 

38 

16 

17 

17 

17 

18 

17 

17 

17 

18 

18 

17 

17 

17 

18 

19 

34 


4 

4 

4 

5 

5 

5 

5 

6 

6 

6 

7 

7 

7 

8 

4 

4 

5 

5 

5 

6 

6 

6 

7 

7 

7 

8 

8 

8 

5 

5 

5 

6 

6 

6 

7 

7 

8 

8 

8 

9 

9 

5 

6 

6 

7 

7 

7 

8 

8 

9 

9 

10 

10 

6 

7 

7 

8 

8 

8 

9 

9 

10 

10 

11 

100%  SCHEDULE  SODIUM  CYANIDE 

Distance  around,  in  feet 
16     18     20     22     24     26     28     30     32     31     36     38     40     42 
10       3       3       3       3       3 
12       3       3       3       3       3       3 

14   333333444445 
16   3   3   33334444455   5 
18   3   3   3   4   4   4   5   5   5   5   5   5   5   6 

4-3 

<S  20  22  24  26  28  30  32  31  36  38  40  42  44  46  48  50 

.2  20  3 

5  22 

6  21 

g  26 
1  28 

CD 

s 

30  32  31  36  38  40  42  44  46  48  50 

30                          7  7   8   8   9  9  10  10  10  11  11 

32  9   9  10  10  11  11  12  12 

34  10  10  11  11  12  12  13 

36  10  11  11  12  12  13  14 

38  11  12  13  13  14  14 


Distance  around,  in  feet 

42  44  46  48  50  52  54  56  58  60  62  64  66  68 

40  13  13  14  14  15  16  16  17  17  18  19  19  20  20 

41  13  14  14  15  15  16  17  17  18  18  19  20  20  21 

42  14  15  15  16  16  17  18  18  19  20  20  21  2.1 

43  15  15  16  17  17  18  19  19  20  21  21  22 

44  17  17  18  18  19  20  20  21  22  22 

50  52  54  56  58  60  62  64  66  68 

45  17  18  18  19  20  20  21  22  22  23 

46  17  18  19  19  20  21  21  22  23  23 

47  18  18  19  20  20  21  22  23  23  24 

48  18  19  19  20  21  22  22  23  24  24 

49  18  18  20  21  21  22  23  24  24  25 


60  62  64  66  68  70  72  74  76 

50  23  23  24  25  26  27  27  28  29 

51  23  25  25  26  27  28  28  29 

52  25  26  27  27  28  29  30 

53  26  27  28  29  29  29  30 

54  28  28  29  30  31 


n 


35 


110%  SCHEDULE  SODIUM  CYANIDE 

Distance  around,  in  feet 
16  18  20  22  21  26  28  30  32  31  36  38  40  42 


10 

3 

3 

3 

3 

3 

12 

3 

3 

3 

3 

3 

3 

14 

3 

3 

3 

3 

3 

3 

4 

4 

4 

4 

4 

5 

16 

3 

3 

3 

3 

4 

4 

4 

4 

4 

5 

5 

6 

6 

18 

3 

3 

3 

4 

4 

4 

5 

5 

5 

5 

6 

6 

6 

6 

6 

6 

6 

7 

7 

7 

8 

8 

9 

9 

6 

6 

6 

7 

7 

8 

8 

9 

9 

9 

9 

6 

6 

"7 

7 

8 

8 

8 

9 

9 

10 

11 

6 

7 

7 

8 

8 

9 

9 

9 

10 

10 

11 

7 

7 

8 

8 

9 

9 

10 

10 

11 

11 

12 

20  22  24  26  28  30  32  34  36  38  40  42  44  46  48  50 

20          3  4   4   5 

22  5   5 

24  5 
26 
28 


30  32  34  36  38  40  42  44  46  48  50  52  54  56  58  60  62  64 

30  7   8   8   9   9  10  11  11  11  12  12  13  13  14  14  14  14  15 

32  10  10  11  11  12  12  13  13  14  14  15  15  16  16  17 

34  11  11  12  12  12  13  14  15  15  16  16  17  17  17 

^  36  11  12  12  13  14  14  15  15  16  17  17  18  18  19 

©  38  12  13  14  14  15  15  16  17  18  18  19  19  20 

> 
o 

<o 

g  42  44  46  48  50  52  54  56  58  60  62  64  66  68 

«  40  14  14  15  15  16  17  17  19  19  20  21  21  22  22 

A  41  14  15  15  16  16  18  18  19  20  20  21  22  22  23 

42  15  16  16  17  18  19  19  20  21  22  22  23  23 

43  16  16  18  18  19  20  21  21  22  23  23  24 

44  18  19  20  20  21  22  23  23  24  24 


50  52  54  56  58  60  62  64  66  68 

45  19  20  20  21  22  22  23  24  24  25 

46  19  20  21  21  22  23  24  24  25  25 

47  2.0  20  21  22  22  23  24  25  26  26 

48  20  21  21  22  23  24  25  25  26  27 

49  20  21  22  23  23  24  25  26  26  27 


60  62  64  66  68  70  72  74  76 

50  25  25  26  27  28  29  30  31  31 

51  25  27  27  28  29  30  31  32 

52  27  28  29  29  31  32  33 

53  28  29  30  31  32  3*3 

54  30  30  32  33  34 


STATION    PUBLICATIONS    AVAILABLE    FOR    DISTRIBUTION 


REPORTS 

1897.      Resistant  Vines,  their  Selection,  Adaptation,  and  Grafting.      Appendix  to  Viticultural 
Report  for  1896. 

1902.  Report  of  the  Agricultural  Experiment  Station  for  1898-1901. 

1903.  Report  of  the  Agricultural   Experiment  Station  for   1901-03. 

1904.  Twenty-second  Report  of  the  Agricultural  Experiment  Station  for  1903-04. 

1914.      Report  of  the   College  of  Agriculture  and  the  Agricultural   Experiment   Station,    July, 
1913-June,    1914. 

BULLETINS 


No. 
168. 

169. 
170. 
174. 
177. 


178. 
182, 


183. 
184. 


185. 


195. 
197. 


198. 
203. 

207. 
208. 
211. 


Observations   on    Some  Vine   Diseases 

in   Sonoma  County. 
Tolerance  of  the  Sugar  Beet  for  Alkali. 
Studies  in  Grasshopper  Control. 
A  New  Wine-Cooling  Machine. 
A   New   Method   of   Making  Dry   Red 

Wine. 
Mosquito  Control. 
Analysis    of    Paris    Green    and    Lead 

Arsenate.    Proposed  Insecticide  Law. 
The  California  Tussock-Moth. 
Report    of    the    Plant    Pathologist    to 

July  1,  1906. 
Report  of  Progress  in  Cereal  Investi- 
gations. 
The  California  Grape  Root-worm. 
Grape  Culture  in  California ;  Improved 

Methods     of     Wine-making;      Yeast 

from  California  Grapes. 
The  Grape  Leaf-Hopper. 
Report    of    the    Plant    Pathologist    to 

July  1,    1909. 
The  Control  of  the  Argentine  Ant. 
The  Late  Blight  of  Celery. 
How  to  Increase  the  Yield  of  Wheat 

in  California. 


No. 

212.  California  White  Wheats. 

213.  The  Principles  of  Wine-making. 
216.  A    Progress    Report    upon    Soil    and 

Climatic     Factors     Influencing    the 

Composition  of  Wheat. 
220.   Dosage  Tables. 

225.  Tolerance  of  Eucalyptus  for  Alkali. 
227.   Grape  Vinegar. 
230.   Enological  Investigations. 
234.   Red  Spiders  and  Mites  of  Citrus  Trees. 

241.  Vine  Pruning  in  California.     Part  I. 

242.  Humus  in  California  Soils. 

243.  The  Intradermal  Test  for  Tuberculosis 

in  Cattle  and  Hogs. 

244.  Utilization  of  Waste  Oranges. 

246.  Vine  Pruning  in  California.     Part  II. 

248.  The  Economic  Value  of  Pacific  Coast 

Kelps. 

249.  Stock  Poisoning  Plants  of  California. 

250.  The  Loquat. 

251.  Utilization    of    the    Nitrogen    and    Or- 

ganic   Matter   in    Septic    and    Imhoff 
Tank   Sludges. 

252.  Deterioration   of   Lumber. 


No. 
65. 
69. 
70. 

76. 
79. 
80. 
82. 

83. 

87. 
88. 


91. 

92. 

100. 
101. 

106. 

107. 
108. 


The  California  Insecticide  Law. 
The  Extermination  of  Morning-Glory. 
Observations   on   the   Status   of   Corn 

Growing  in  California. 
Hot  Room  Callusing. 
List  of  Insecticide  Dealers 
Boys'   and   Girls'   Clubs. 
The    Common    Ground    Squirrels    of 

California. 
Potato  Growing  Clubs. 
Alfalfa. 
Advantages  to  the  Breeder  in  Testing 

his  Pure-bred  Cows  for  the  Register 

of  Merit. 
Disinfection  on  the  Farm. 
Infectious    Abortion    and    Sterility    in 

Cows. 
Pruning  Frosted  Citrus  Trees. 
Codling   Moth    Control    in    the    Sacra- 
mento Valley. 
Directions  for  using  Anti-Hog-Cholera 

Serum. 
Spraying  Walnut  Trees  for  Blight  and 

Aphis    Control. 
Grape  Juice. 


CIRCULARS 

No. 
109. 


Community  or  Local  Extension  Work 
by  the  High  School  Agricultural  De 
partment. 

110.  Green  Manuring  in  California. 

111.  The  Use  of  Lime  and  Gypsum  on  Cali 

fornia  Soils. 
13.   Correspondence  Courses  in  Agriculture. 

114.  Increasing  the  Duty  of  Water. 

115.  Grafting  Vinifera  Vineyards. 

117.  The    Selection    and    Cost    of    a    Small 

Pumping  Plant. 

118.  The  County  Farm  Bureau. 

119.  Winery  Directions. 

121.  Some    Things    the    Prospective    Settler 

Should  Know. 

122.  The  Management  of   Strawberry   Soils 

in  Pajaro  Valley. 

123.  Fundamental    Principles    of    Co-opera 

tion  in  Agriculture. 

124.  Alfalfa  Silage  for  Fattening  Steers. 

125.  Aphids  on  Grain  and  Cantaloupes. 

126.  Spraying  for  the  Grape  Leaf  Hopper. 

127.  House   Fumigation. 

128.  Insecticide  Formulas. 


